Chapter 8. Compounding with Chlorinated Polyethylene

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8.2 INFLUENCE OF CPE CHEMICAL STRUCTURE

8.2.1 SATURATED BACKBONE

A generalized chemical structure for CPE is shown (Figure 8.1). The ASTM D1418

designation for CPE is ‘‘CM’’ where ‘‘C’’ denotes ‘‘chloro’’ and ‘‘M’’ denotes ‘‘a

saturated chain of the polymethylene type.’’ CPE and CM are often used interchangeably in the industry. In this chapter, the term CPE is used.

The saturated backbone of CPE imparts outstanding ozone-, oxidative-, and

heat-resistance to a compound’s performance [4]. The inherent nature of the polymer

backbone allows compounds of CPE to be formulated that meet stringent high heat

requirements, for example, up to 1508C for certain automotive applications and 1058C

for various wire and cable applications using a peroxide cure system [5]. CPE typically

provides better heat-aging resistance than polymers containing backbone unsaturation,

for example, natural rubber and polychloroprene (CR) (Figure 8.2).



8.2.2 CHLORINE CONTENT

Typical commercial grades of CPE contain from 25 to 42 wt% chlorine (Table 8.1).

The addition of chlorine to the backbone creates polarity in the polymer structure

that imparts oil- and chemical-resistance to the polymer and subsequently to the

compounded material. In addition, the chlorine on the backbone can help provide

inherent flame retardance by providing a halogen source in a fire situation [6]. This is

often advantageous for the compounder, for example, it may not be necessary to add

a costly halogen-containing flame-retardant additive to the formulation if the recipe

includes a CPE that contains a sufficiently high level of chlorine. However, as the

compounder knows, to obtain one property, another is often sacrificed. In the case of

chlorine content, it is necessary to balance the flame-retardant properties with the

low-temperature performance (Figure 8.3).



8.2.3 VISCOSITY

The molecular weight of the polyethylene feedstock plays a key role in determining

the viscosity of the CPE product. Higher molecular weight feedstocks, that is, those

with low melt index (I2) values, yield CPE resins with higher Mooney Viscosity

values. For a given polyethylene I2, other parameters directly affect viscosity, for

example, MWD and comonomer type. The use of broader or narrower MWD

polyethylene resins coupled perhaps with a copolymer of ethylene with, for example,

butene, hexene, or octene, can provide a wide range of CPE viscosities. In addition,

the chlorine content of the CPE resin can also affect the viscosity of the CPE. For a

given polyethylene feedstock, the CPE viscosity increases with chlorine content.



—



— CH2— CH— CH2— CH2— CH2—

Cl



FIGURE 8.1 Generalized chemical structure of CPE (~36 wt% chlorine).



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Compounding with Chlorinated Polyethylene

Type °C



°F



H



250



G



225



437



F



200



392



E



175



347



D



150



302



C



125



257



B



100



212



A



70



Fluoroelastomer



482



158



Silicone

Fluorosilicone



Ethylene

octene



CPE

CSM



Polyacrylate



EPDM

Butyl



CR



Nitrile



Epichlorohydrin



Styrene butadiene

Natural rubber



Increasing heat resistance

Class No Req. 170 120 100 80 60 40 20 10

A

B C D E F G H K

Increasing oil resistance



FIGURE 8.2 Heat and oil resistance of various elastomers (ASTM 2000=SAE J-200

Classification).



TABLE 8.1

Typical Commercial Grades of CPE for Elastomer Applications

Product



Chlorine

Content,a

wt%



Mooney Viscositya

Crystallinity (ML1 1 4 at 1218C),

Mooney Units

Ha, J=g

f



Specific

Gravity



TYRINTM CM 0136



36



<2



80



1.16



TYRINTM CM 0836



36



<2



94



1.16



TYRINTM CM 566



36



<2



80



1.16



TYRINTM CM 0730



30



<2



65



1.14



TYRINTM 3611P



36



<2



30



1.16



TYRINTM 4211P



42



<2



42



1.22



Note:



a



TM



Key Properties

General purpose

elastomer grade

General purpose

elastomer=high

molecular weight

Low electrolyte

grade

Best balance of

low and high

temperature

performance

Good for viscosity

modification

Higher chlorine

viscosity

modification



is the Trademark of The Dow Chemical Company. Other product grades are available. Contact the

polymer producers for additional product information. The Dow Chemical Company is the only North

American producer of chlorinated polyethylene. Other producers of chlorinated polyethylene include

Showa Denko (Japan), Osaka Soda (Japan), and Weifang (China).



Reported values represent typical measurements.



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Low-temperature

flexibility



Oil-, solvent-, and

flame-resistance



Increasing

performance

property

Increasing chlorine content



FIGURE 8.3 Effect of increasing chlorine content on various properties.



Manufacturers of CPE have the ability to use several variables to produce a range of

CPE viscosities for the compounder to use (Table 8.1).



8.3 COMPOUNDING WITH CPE

8.3.1 INTRODUCTION



TO



COMPOUNDING



CPE, like most elastomers, needs to be properly ‘‘compounded’’ or ‘‘formulated’’ to meet

the product performance requirements for any given application. The process of selecting

types and levels of compounding ingredients can involve a complex combination of

factors for the CPE compounder developing a formulation. Factors to consider include:

1. CPE Polymer type

. Viscosity

. Chlorine content

. Residual crystallinity

. Additives

2. Performance requirements

. Original and aged physical properties

. Processing

. Electrical properties (where applicable)

. Applicable standards, for example, automotive, wire and cable

3. Thermoset or thermoplastic application

4. Safety

. Environmental issues

. Industrial hygiene issues

5. Compounding ingredients

. Black or colorable compound

. Cure system

. Proper selection to meet necessary performance requirements

6. Total cost of producing the final article

The consideration of these factors (and others) in the development of a suitable

compound for a particular application can be a difficult task. The effects of various



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Compounding with Chlorinated Polyethylene



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compounding ingredients on physical properties can usually be easily measured in

the laboratory, but conducting trials at the production level is a critical step of the

compound development process. The production trial reveals factors that may not

have been predicted in the lab, for example, property differences due to scale-up in a

larger extruder. The compounder can make modifications and refinements to the

compound based on information from the factory experience.

General references on the subject of ‘‘compounding’’ elastomers can be found in

the literature and usually cover a broad range of polymers [7–9]. In this section, the

compounder is provided with information on factors to be considered in developing a

CPE recipe for typical applications. Specific starting-point formulations for various

applications are included later in this report and in the literature [10].



8.3.2 COMPOUNDING INGREDIENTS



AND



THEIR FUNCTION



The list of ingredients available to the compounder is quite impressive and can

sometimes be overwhelming [11]. Most CPE formulations contain one or more

ingredients from each of the following categories:

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.



CPE

Fillers

Acid acceptors

Colorants

Plasticizers

Flame retardants

Antioxidants

Processing aids

Curatives

Coagents



A summary of several of the generic compounding ingredients and their function is

included (Table 8.2). As noted, certain ingredients are specific to the cure system that

is used. Undesirable chemical reactions can interfere with the curing mechanisms or

even with the stability of the base polymer. For example, zinc-containing compounds, for instance, zinc oxide, should be avoided in all CPE compounds. Zinc

oxide can cause dehydrochlorination of the CPE (regardless of the type of cure

system) resulting in degradation of the polymer structure and a subsequent reduction

in physical property performance. In addition, small quantities of zinc can adversely

affect the cure mechanism in thiadiazole-cured compounds. The CPE manufacturer

should be contacted for additional information on interactions=potential interactions

of various compounding ingredients.

8.3.2.1



Choosing a CPE



The initial step in developing a CPE recipe typically involves the selection of the

proper base polymer. Some of the most important variables to consider in a CPE

product are viscosity, chlorine content, and degree of residual crystallinity.



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TABLE 8.2

Compounding Ingredients and Their Function

Ingredienta



Function

Acid acceptor

Coagents or accelerators

Colorant

Filler

Flame retardant

Plasticizers

Processing aids

Vulcanizing (curing) agents

Antioxidants

a



Magnesium oxide, magnesium hydroxide, calcium hydroxide,

epoxy compounds, lead compounds

Allylic, methacrylate

Carbon black, titanium dioxide, organic pigments

Carbon black, mineral

Antimony oxide, hydrated alumina, halogenated hydrocarbons

Petroleum oils (aromatic and napthenic), esters, chlorinated paraffins,

polymeric polyesters

Waxes, stearic acid, low molecular weight polyethylene, EPDM, EVA

Peroxide, thiadiazole, electron beam

Variety of oxidative stabilizers are suitable



Some ingredients are cure-system specific.



8.3.2.1.1 CPE Viscosity

The viscosity of CPE is typically influenced by a combination of the molecular

weight of the starting polyethylene and the level of chlorine added to the polyethylene. The combination of these factors contributes to the viscosity of the CPE, as

measured by such tests as Mooney viscosity or capillary rheology. In general, the

viscosity of CPE is controlled by the combination of the polyethylene feedstock

molecular weight and the amount of chlorine added to the polyethylene backbone.

However, other factors can affect the viscosity such as the MWD of the polyethylene, additives in the final CPE product, and the presence of residual crystallinity.

When developing a new formulation, the compounder may be uncertain about

which viscosity to choose in the initial formulations. A good starting-point for most

general purpose, thermoset CPE compounds is an amorphous product, that is,

essentially no residual crystallinity, with a Mooney viscosity (ML1 þ 4 at 1218C)

of around 75–80 and a chlorine content of 36 wt%. This starting-point CPE product

generally provides a compound with suitable physicals and good processability.

However, the compounder can evaluate the mechanical properties and processability

characteristics to determine if a CPE product with higher or lower viscosity is needed

to fulfill the desired application requirements. Blends of different CPE grades can

be used to provide additional processability or physical property advantages. CPE

is also compatible with a variety of other elastomers and thereby provides an

additional method of tailoring the processability and physical property characteristics

in polymer blends.

8.3.2.1.2 Chlorine Content

The chlorine content of commercial grades of CPE typically ranges from 25 to 42

wt% chlorine. The chlorine content of the resin is an important choice for the

compounder. CPE resins with ~36% chlorine are most commonly used for thermoset



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Compounding with Chlorinated Polyethylene



295



elastomeric applications. This level of chlorine in the CPE typically provides a

vulcanizate that possesses a good balance of chemical and oil resistance, flame

retardance, low-temperature performance, processability, and good response to a

peroxide cure system. If additional flame-, chemical-, or oil-resistance is desired, it

may be necessary to use a CPE with higher chlorine content, for example, a 42%

chlorine product. To achieve a balance between oil-, chemical-, and flame-resistance

and good low- and high-temperature performance, 30% chlorine content amorphous

CPE can provide a vulcanizate with suitable performance. CPE resins with even

lower chlorine content (25% chlorine) are also available. Usually, the 25% chlorine

grades contain residual polyethylene crystallinity that improves the compatibility

when blended with other polymers such as polyethylene.

8.3.2.1.3 Residual Crystallinity

The parameters in the CPE production process allow the producer to tailor-make the

desired degree of residual crystallinity in the final product. For thermoplastic applications of CPE or for applications requiring higher degrees of compatibility with another

polymer such as polyethylene, it is often desirable to use a CPE that contains some

portion of the original high-temperature crystallinity (melting point ~1258C–1308C) of

the polyethylene. This crystallinity imparts stiffness to the CPE and thereby yields a

higher modulus material. The resultant ‘‘polyethylene-type’’ characteristics in these

semicrystalline CPE products can be used to good advantage when one blends the

resin with high-ethylene content polymers to improve compatibilization.

Most CPE products are designed to be amorphous, that is, they contain essentially no residual crystallinity from the high-temperature portion of the polyethylene.

This yields an elastomer with more rubbery qualities and the resultant products find

use in a wider variety of applications than do the semi-crystalline CPE products.

8.3.2.2



Curatives



Cure agents for CPE compounds are typically based on (1) peroxide cure systems

with coagents; (2) thiadiazole-based chemistries; or (3) irradiation cross-linking

techniques [12,13]. The choice of cure system depends upon a number of factors

such as compound cost, processing equipment, and curing equipment.

Peroxide cures are preferred when extra scorch safety, shelf-life, or bin stability,

low-permanent set, and high-temperature performance are desired. Thiadiazole cure

provides the ability to cure over a wider range of temperature and pressure conditions

while generating fewer volatile by-products than do peroxide cures. Irradiationcurable compounds are usually formulated in a similar manner to the peroxide-curable

compounds except that no peroxide is necessary.

8.3.2.3



Fillers, Plasticizers, Other Ingredients



Fillers are used in CPE compounds for the same reasons they are used in most rubber

compounds—fillers provide a means of obtaining a good balance between the

necessary physical property characteristics and the economic requirements of the

end-use article. The fillers used with CPE are common to the rubber industry: carbon

black and mineral fillers (clay, whiting, talc, silica, etc.).



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A variety of plasticizers are compatible with CPE. The most commonly used

plasticizers include the ester-types. The type of plasticizer that can be used is often

dependent upon the cure system. For example, aromatic plasticizers typically are not

used in peroxide-cured recipes (due to hydrogen abstraction of the aromatic protons),

whereas the aromatic plasticizers can be used effectively with the thiadiazole-cured

compounds.

The final recipe usually includes a stabilizer, such as MgO or some similar acid

acceptor. Other common rubber compounding ingredients are usually added to meet

the physical property and processing requirements of the compound.



8.4 END-USE APPLICATIONS

Starting-point formulations for CPE compounds are available from polymer producers and the open literature [10]. End-use elastomeric applications for CPE are wideranging, for example, Wire and Cable, Automotive, Industrial, and General Rubber

markets. CPE is also widely used in the Impact Modification market segment to

improve the performance of vinyl siding and other vinyl-related products [14].

To aid the user in understanding typical CPE elastomer formulations, examples

from different market segments are included (Tables 8.3 through 8.5). A wide

range of performance can be achieved using CPE elastomers. The compounder is

encouraged to explore the possibilities available with CPE: Oil Resistance, Ozone

Resistance, Weatherability, Oil and Chemical Resistance, Heat-Aging Resistance,

Low-Temperature Flexibility, Processability, Blend Additive, and more.

TABLE 8.3

Typical CPE ‘‘HPN Heater Cord’’ Jacket (908C Rating)

Ingredient



phr



TYRINTM CM 0136

Calcium carbonate

Diisononyl phthalate

Amino silane-functionalized hydrated aluminum silicate

Magnesium oxide

Polymerized 1,2-dihydro 2,2,4-trimethylquinoline

a, a0 -Bis-(tert-butylperoxy)-diisopropylbenzene

dispersed on clay (40% active)

85% Antimony oxide on CM binder

Trimethylolpropane trimethacrylate

Total phr



6

5

256.2



Specific gravity



1.55



100

50

25

60

5

0.2

5



Stock properties

Mooney scorch MS þ 1 at 1218C (ASTM D1646)

Minimum viscosity, Mooney units

t3 (time to 3-unit rise), minutes

t5 (time to 5-unit rise), minutes



CPE Compound

30.1

>25

>25



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Compounding with Chlorinated Polyethylene



TABLE 8.3 (Continued)

Typical CPE ‘‘HPN Heater Cord’’ Jacket (908C Rating)

Ingredient

ODR at 2048C, 0.051 rad, 1.66 Hz, microdie, 6 min (ASTM D2084)

Minimum torque, ML, dN-m

12.2

Maximum torque, MH, dN-m

64.1

Delta torque, dN-m

55.3

Time to 90% Cure (t90), minutes

1.8

Vulcanizate properties

1.16 mm Insulation on 14 AWG aluminum wire

Cured 2 min in 1.72 MPa gauge steam

Original stress–strain properties

Stress at 100% elongation, MPa

Stress at 200% elongation, MPa

Tensile strength at break, MPa

Elongation at break, %

Air-oven aged 10 days=1108C

Tensile retention, %

Elongation retention, %

IRM 902 Oil immersion 18 h at 1218C

Tensile retention, %

Elongation retention, %

Note:



TM



UL 62, 2.5 specification



8.2 minimum

200 minimum



CPE compound

4.9

9.0

15.8

402



50 minimum

50 minimum



105

85



60 minimum

60 minimum



97

78



is the trademark of The Dow Chemical Company.



TABLE 8.4

Moisture, Flame-Resistant, Lead-Free, Heavy Duty Cable Jacket (908C)

Ingredient

TYRINTM CM 566

Carbon black N550

Calcined and surface modified clay

Dioctyl adipate

Dow epoxy resin (D.E.R.TM 331)

Thiodiethylene bis-(3,5-di-tert-butyl-4-hydroxy)hydrocinnamate

a,a0 -Bis-(tert-butylperoxy)-diisopropylbenzene

dispersed on clay (40% active)

85% Antimony oxide on CM binder

80% Decabromodiphenyl oxide on CM binder

Trimethylolpropane trimethacrylate

Total phr=specific gravity



phr

100

5

60

15

5

1.5

5

7

15

5

218.5=1.45

(continued )



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TABLE 8.4 (Continued)

Moisture, Flame-Resistant, Lead-Free, Heavy Duty Cable Jacket (908C)

Ingredient



phr



Stock properties

Mooney scorch MS þ 1 at 1218C (ASTM D1646)

Minimum viscosity, Mooney units

t3 (time to 3-unit rise), minutes

t5 (time to 5-unit rise), minutes



CPE compound

26.3

>25

>25



ODR at 2048C, 0.051 rad, 1.66 Hz, microdie, 6 min (ASTM D2084)

Minimum torque, ML, dN-m

11.1

Maximum torque, MH, dN-m

57.3

Delta torque, dN-m

46.2

1.9

Time to 90% cure (t90), minutes

Vulcanizate properties

1.16 mm Insulation on 14 AWG aluminum wire

Cured 2 min in 1.72 MPa gauge steam

Original stress–strain properties



Stress at 100% elongation, MPa

Stress at 200% elongation, MPa

Tensile strength at break, MPa

Elongation at break, %

Air-oven aged 7 days=1008C

Tensile retention, %

Elongation retention, %

IRM 902 Oil immersion 18 h at 1218C

Tensile retention, %

Elongation retention, %

Note:



TM



ICEA S-68–516

4.4.11, ICEA

S-19–81 4.13.11

specification



CPE compound



3.45 minimum

12.4 minimum

300 minimum



4.1

8.8

17.4

522



85 minimum

55–65 minimum



103

83



60 minimum

60 minimum



70

81



is the trademarks of The Dow Chemical Company.



TABLE 8.5

CPE Molded Goods Compound

Ingredient



phr



TYRINTM CM 0136

Carbon black N550

Silica

Trioctyl trimellitate (TOTM)

Thiadiazole curative

Amine accelerator for thiadiazole cure

Magnesium hydroxide



100

50

10

35

3

1

5



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Compounding with Chlorinated Polyethylene



TABLE 8.5 (Continued)

CPE Molded Goods Compound

Ingredient



phr



Styrenated diphenylamines antioxidant

Hindered phenolic antioxidant=metal deactivator

Total phr



1

1

206



Specific gravity



1.28



Compound properties

Mooney scorch MS þ 1 at 1218C (ASTM D1646)

Minimum viscosity, Mooney units

t3 (time to 3-unit rise), minutes



38

>25



ODR at 1608C, 0.051 rad, 1.66 Hz, microdie, 30 min (ASTM D2084)

Minimum torque, ML, dN-m

12.5

Maximum torque, MH, dN-m

52.0

Delta torque, dN-m

39.5

Time to 90% cure (t90), minutes

13.0

Vulcanizate properties

Original stress–strain properties

(Cured 20 min at 1608C)

Stress at 100% elongation, MPa

Stress at 200% elongation, MPa

Ultimate tensile, MPa

Elongation, %

Hardness, shore A

Die C Tear, ppi at 238C

Die C Tear, ppi at 1608C

Low-temperature brittleness, 8C

Compression set 22 h=1008C, %

Ozone resistance, cured 5 min at 1828C

72 h at 408C, 100 pphm ozone, 55% humidity

Aged in air oven 70 h at 1508C

Tensile change, %

Elongation change, %

Note:



TM



CPE

3.8

7.6

18.0

530

78

302

107

À34

26

Pass—no cracks

À9

À48



is the trademark of The Dow Chemical Company.



REFERENCES

1. U.S. Patent 3,454,544, Process for the Chlorination of Polyolefins, Issued July 8, 1969 to

Dow Chemical U.S.A.

2. U.S. Patent 3,429,865, Chlorinated Polyethylene Compositions, Issued February 25,

1969 to Dow Chemical U.S.A.

3. U.S. Patent 3,563,974, Linear Polyethylene Chlorination, Issued February 16, 1971 to

Dow Chemical U.S.A.



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4. W.H. Davis, Jr., R.L. Laakso, Jr., L.B. Hutchinson, and S.L. Watson, Peroxide-Cured

Chlorinated Polyethylene Compounds Having Enhanced Resistance to Ozone-Induced

Cracking, American Chemical Society Rubber Division, May 29–June 1, 1990, Paper No. 8.

5. R.R. Blanchard, Compounding Chlorinated Polyethylene Elastomers for High Temperature

Service, Advances in Synthetic Rubbers and Elastomers Science and Technology, Technomic Publishing Co., Inc., 1973, pp. 1–13.

6. R.M. Aseeva and G.E. Zaikov, Combustion of Polymer Materials, Hanser Publishers,

Munich Vienna, New York, 1985, pp. 214–219.

7. F.W. Barlow, Rubber Compounding, Second Edition, Marcel Dekker, Inc., New York,

1993.

8. J.E. Mark, B. Erman, and F.R. Eirich, Science and Technology of Rubber, Second

Edition, Academic Press, Inc., San Diego, CA, 1994, Chapter 9.

9. M. Morton, Rubber Technology, Third Edition, Van Nostrand Reinhold, New York,

1987.

10. P.A. Ciullo and N. Hewitt, The Rubber Formulary, Noyes Publications, Norwich, New

York, 1999, pp. 579–597.

11. Rubber World Magazine’s Blue Book 2002, J.H. Lippincott, publisher, Lippincott &

Peto Inc.

12. L.E. Sollberger and C.B. Carpenter, ‘‘Chlorinated Polyethylene Elastomers—A Comprehensive Characterization,’’ presented at a meeting of the Rubber Division, American

Chemical Society, Toronto, Canada, May 7–10, 1974.

13. J.H. Flynn and W.H. Davis, ‘‘Tyriny Brand CPE Thiadiazole Cure System Studies—

Chemistry and Dispersion,’’ presented at a meeting of the Rubber Division, American

Chemical Society, Los Angeles, California, April 23–26, 1985.

14. Polymeric Materials Encyclopedia, Volume 2=C, CRC Press, 1996, Editor-in-Chief

J.C. Salamone, chapter on ‘‘Chlorinated Polyethylene,’’ G.R. Marchand.